The present invention relates to a piezoelectric transformation circuit driver module for driving multiple loads in a stable fashion.
Liquid Crystal Display (LCD) panels for desk top or notebook computers, PDAs, and Webpads now available on the market all require a light source. The light source is generated by a driver device to actuate a cold cathode fluorescent lamp (CCFL) at a high voltage to project light on a back light panel to produce visible display pictures. In addition, ozone generators and negative ion generators also employ high voltage to drive the element or device to achieve sterilization effect.
Furthermore, LCD TVs or LCD display screens that that have touch control films require stronger light intensity to compensate visual viewing requirements. A CCFL is lighted at a high voltage. A stronger electric current can generate a stronger light intensity. In order to increase light intensity and evenness, a plurality of lamp tubes are usually being used. In such an environment, evenness of tube currents or small characteristics deviations among the lamp tubes become very important. In addition, when there are multiple loads, control elements for driving lighting also increase. As a result, circuit boards become bigger and manufacturing becomes more difficult and costs increase. FIG. 1 illustrates a conventional driver device for actuating a CCFL. When the voltage of a power supply unit 3 is applied, the driver unit 5 immediately actuates a piezoelectric ceramic transformer 1 to light a CCFL 2 through a reverse/positive piezo-effect. A pulse-width modulation (PWM) control unit 4, through current feedback 7, detects tube electric current in the lamp tube 2. And average current of the CCFL 2 may be controlled through the driver unit 5 and the piezoelectric transformer 1. Light being generated may be projected to the back light panel to display pictures.
However, when employing a plurality of lamp tubes to augment light intensity and evenness, as every lamp tube has allowances and deviations during production, electric current and light intensity of every lamp tube are different. To select and match multiple numbers of lamp tubes to improve light intensity and evenness is troublesome or requires additional lamp tubes. It incurs greater costs, and also is not easy to produce or adjust.
There is a prior art disclosed in Japan Patent No. 11-259028 which adopts a driving method. It functions by inputting a pair of voltages of opposite phases in input ends of two piezoelectric transformers. The piezoelectric transformer has output ends to deliver a pair of voltages of opposite phases for driving use. However in practice, to adopt on circuits by making a pair of voltages of opposite phases to connect to the input ends of piezoelectric ceramic transformers makes the driving circuit too complicated and costly. It is also difficult to produce. Moreover, the circuit utilizes an electromagnetic transformer as a current detector which incurs electromagnetic interference (EMI) problems. As a result, the advantage of employing the piezoelectric ceramic transformers without EMI problems is lost.
Therefore the primary object of the invention is to resolve aforesaid disadvantages. The invention provides a piezoelectric transformation circuit including a pair or pairs of piezoelectric ceramic transformers connecting to one or more loads. Each pair of voltages of the same phase are input to a pair of input ends which have opposite polarization, or the two piezoelectric ceramic transformers group have input ends of opposite polarization or its group assembly output an even number of output voltages with opposite phases to two end of a load, or input ends of the loads which the feedback ends are coupled together in series. When driven by the piezoelectric transformation circuit, and with voltage applying on the loads, improved characteristics such as even output current, greater output power and better matching impedance can be obtained. And a single driver circuit can actuate multiple sets of loads simultaneously in a stable fashion.
Another object of the invention is to connect with capacitor(s) to the input end(s) of the piezoelectric ceramic transformer(s) to form a branch capacitance to compensate oscillation of the piezoelectric ceramic transformer to obtain more energy (to increase load current). The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.